There is a great need of catalyst compounds that are suitable for the polymerization of olefins in the presence of polar additives.
The polyolefin industry employs processes in which ethene as well as other non-polar 1-olefins are polymerized with the aid of various catalysts and free-radical initiator systems. Such polymerizations may be carried out by the use of organometallic Ziegler-Natta co-ordination catalysts, chromium catalysts and, most recently, with metallocene-like compounds of early transition metals, and also free-radical initiators. In addition it is found that these catalysts react in a very sensitive manner to a range of substances that adversely affect or completely inhibit the catalytic activity. For example, it is known that traces of oxygen, carbon monoxide, water or oxygen-containing organic compounds that act as donors can lead to a deactivation of these catalysts. If such substances are present the use of catalysts is normally restricted to free-radical initiator systems.
In order to improve this situation and also to co-polymerize polar monomers, catalysts based on late transition metals have been developed. Review articles may be found in Mecking, S. Angew. Chem. 2001, 113, 550; Ittel, S., Johnson, L. K. and Brookhart M. Chem. Rev. 2000, 100, 1169 and Boffa, L. S.; Novak, B. M. in Chem. Rev. 2000, 100, 1479.
The types of complexes used are typically subdivided into those with anionic ligand skeletons or those with neutral ligand skeletons. The group of complexes with an anionic ligand skeleton exhibit on account of the uncharged, (neutraly active polymerization species particularly robust properties with respect to the catalyst poisons mentioned above. The reason for this is the reduced Lewis acidity of the catalytic species. Current research is therefore concentrated specifically on such types of catalyst. Thus, Ostoja Starzewski and K. A. Witte describe in J. Angew. Chem. 1987, 99, 76 such catalysts with a [P,O] ligand type. Klabunde, U. and Ittel, S. D. also report on similar catalysts in J. Mol. Catal. 1987, 41, 123. Comparable catalysts with [P,O] complexes are also disclosed in U.S. Pat. No. 5,175,326.
A new catalyst class A conceptually similar to [P,O] complexes has also been developed, which contains an imine nitrogen donor instead of the phosphorus donor.
The common feature is large steric radicals R and R″″, which screen as far as possible the apical positions around the metal centre.
The corresponding processes for the production of such catalysts are described in more detail in WO 98/30609, WO 98/42664, WO 98/42665, DE-A 199 61 340, WO 00/56785, WO 01/92347 and WO 02/08236.
It was now surprisingly found that special azo dyes can also be incorporated into a number of anionic ligand systems for purposes of complexing. Azo dyes represent a class of compounds that has already been investigated in detail, and which in addition can be synthesized on an industrial scale.
Such ligands for the production of single-site catalysts for the polymerization of olefins are disclosed by Schroder, D. L., Keim, W., Zuideveld, M. A., Mecking, S. in Macromolecules, 2002, 35, 6071. Activation with widely different Lewis acids in the presence of polar additives as well as sterically demanding ortho-substituted compounds that have a specific influence on the activity and molecular weight are not disclosed however.
In EP-A 1 170 308 ligands are described that likewise exhibit an azo finction but, in contrast to the claimed complexes, do not have an oxygen-metal bond but instead have an amide-type nitrogen-metal bond. Also, no transition metal compounds with late transition elements are disclosed. No sterically demanding substituents in the ortho position to the amide-type nitrogen in such complexes are described.
DE-A 123747 disclosed a monometallic, chelating azo ligand that has, in addition to the azo donor function, a metal-carbon(phenyl) bond, i.e. not an oxygen-metal bond but a carbanionic phenyl-metal bond. Since metal-phenyl bonds of nickel have been shown to be polymerization active, the complex postulated in DE-A 123747 would not co-ordinate the metal centre in a chelate-type manner during the polymerization. The disadvantage with this process is therefore the change in the geometry of the metal complex during the polymerization. Accordingly good results are not expected as regards the uniformity of the polymers.